The present invention relates to a type of circuit known as a programmable logic array. Typically, programmable logic or very large scale integrated circuit (VLSI) circuit chips. These programmable logic array chips are of a type that when manufactured, the particular logic function of the circuit is not determined. A programmable logic array chip is designed so that the logic function of the chip may be subsequently determined. Most of such prior art chips are hard programmable in that they contain fuses or other elements which are permanantly burned or blown out in order to determine the logic function of the device. The present invention relates to a soft programmable device in that any particular device may be repeatedly programmed with the same or with different logic functions through a process of inputting logic functional data, which is sometimes known as characterization data. Although a soft programmable logic array requires the loading of characterization data in order to function, the logic array of the present invention is not merely a memory device. The characterization data is used to control the particular logic functions to be performed at particular logic levels in the array. In addition, chips according to the present invention are arranged with four quadrants or sectors and control circuitry on each chip so that several independent arrays are on one chip with common functional control.
Known to applicant in the prior art is U.S. Pat. No. 3,818,252 which shows a plurality of word lines and digit lines as inputs to an array which contains fuses for the programmable elements. This patent shows, in effect, a variation of a standard programmable logic array having two levels for the production of a sum of products type of function, but does not anticipate the present multi-level soft programmable logic array. U.S. Pat. No. 4,233,667 also shows a programmable logic array, but which does not anticipate the present invention in structure or capability.
U.S. Pat. No. 3,912,914 shows a programmable switching module which can become extremely complex for any particularly large switching function to be employed since the programming control for any switching function must be brought off the particular chip by individual wires to control the switching function. The present invention is programmed by inserting a stream of characterizing data which controls the various logic elements as a result of a characterizing process. Other patents known to applicant in the prior art are U.S. Pat. Nos. 3,855,536, 3,976,983 and 4,293,783, all of which show logic arrays but which either require programming control through external logic pins or which have limitations on the particular logic functions that may be accomplished.